Objective: The overall objectives of this research proposal are (1) to determine whether DMBA-induced rat mammary tumors are capable of producing estrogen which acts directly interaction between estrogen and mammary tumor tissue especially in regard to the regulation of tumor growth. The folllowing propose hypotheses are the main basis for the construction of different experiments in this study; 1. DMBA- induced mammary tumor in rats acts as a para-endocrine organ and is capable of producing estrogen to modify its own hormol environment and to influence the regulation of tumor growth. 2. In DMBA-induced mammary tumor, the level of specific estrogen binding capacity (or estrogen receptor) varies with different endocrine conditions. It is possible to reduce this level by suitable hormonal treatments. 3. In DMBA- induced mammary tumor, the binding of estrogen by the tumor tissue is the rate limiting factor in the process of estrogen action; that its, the amount of estrogen-receptor complex in the tissue regulates the degree of response to estrogen stimulation by the tumor. Methods: Mammary tumors will be induced in Sprague-Dawley rats by a single feeding of DMBA. Different approaches in methodology will be employed. The highlights of these approaches are the following: 1. To study in vitro synthesis of estrogen by DMBA-induced mammary tumors. 2. To determine the specific binding of estrogen by DMBA-induced mammary tumors from ovariectomized animals treated with different hormones. 3. To examine the vitro incroporation of amino acids by DMBA- induced mammary tumors and the effect of estrogen stimulation on this incorporation.